The present invention relates generally to inkjet printing mechanisms, and more particularly to a grooved wiper blade tip for wiping ink residue from inkjet printheads, and especially for cleaning printheads having surface irregularities such as encapsulant beads, which are required to assemble the printhead.
Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as xe2x80x9cink,xe2x80x9d onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a xe2x80x9cservice stationxe2x80x9d mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. To facilitate priming, some printers have priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as xe2x80x9cspitting.xe2x80x9d The waste ink is collected at a spitting reservoir portion of the service station, known as a xe2x80x9cspittoon.xe2x80x9d After spitting, uncapping, or occasionally during printing, most service stations have a flexible wiper, or a more rigid spring-loaded wiper, that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. Unfortunately, the combination of small nozzles and quick-drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves. Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, keeping the nozzle face plate clean becomes even more important when using pigment based inks, because they tend to accumulate more debris than the earlier dye based inks.
Indeed, keeping the nozzle face plate clean for cartridges using pigment based inks has proven quite challenging. These pigment based inks require a higher wiping force than that previously needed for dye based inks. Yet, there is an upper limit to the wiping force because excessive forces may damage the orifice plate. Thus, a delicate balance is required in wiper design to adequately clean the orifice plate to maintain print quality, while avoiding damage to the nozzle plate itself.
Many previous wiping solutions used a cantilever wiping approach. In cantilever wiping, a flexible, low durometer elastomeric blade is supported at its base by a sled. While the sled may be stationary, in many designs it was moveable so the sled could travel to a position where the wipers engage the nozzle plate. Wiping was accomplished through relative motion of the wipers with respect to the nozzle plate, by either moving the wiper relative to a stationary nozzle plate, or by moving the nozzle plate relative to a stationary wiper. The earlier wiper positioning mechanisms included sled and ramp systems, rack and pinion gear systems, and rotary systems.
The flexibility of the cantilever wiper accommodates for variations in the distance between the nozzle plate and sled, also referred to as variations in the xe2x80x9cinterferencexe2x80x9d between the wiper and nozzle plate. That is, for a closer sled-to-nozzle spacing (or a xe2x80x9cgreater interferencexe2x80x9d), the wiper flexed more than it would for a larger spacing. The force transmitted to the face plate was determined by the degree of bending of the wiper blade, as well as by the stiffness of the wiper blade material. The stiffness of the wiper blade is a function of the geometry of the blade and of the material selected. For instance, one common measure of elastomeric flexibility (tested using a sample of a standard size) is known as the xe2x80x9cdurometer,xe2x80x9d including a variety of scales known to those skilled in the art, such as the Shore A durometer scale.
Besides focusing on the material selection for inkjet wipers, other research has investigated changing the contour of the wiper tip which contacts the printhead orifice plate. A revolutionary rotary, orthogonal wiping scheme was first used in the Hewlett-Packard Company""s DeskJet(copyright) 850C color inkjet printer, where the wipers ran along the length of the linear arrays, wicking ink from one nozzle to the next. This wicked ink acted as a solvent to break down ink residue accumulated on the nozzle plate. This product used a dual wiper blade system as shown in FIGS. 7 and 8, where wiper blades W1 and W2 project from a supporting sled S. The wiper blades W1 and W2 have special contours at their tips to facilitate this wicking action and subsequent printhead cleaning. Each blade W1 and W2 has an outboard rounded edge R and an inboard angular wiping edge A. The rounded edges R encounter the nozzles first and form a capillary channel between the blade and the orifice plate to wick ink from the nozzles as the wipers moved orthogonally along the length of the nozzle arrays. The wicked ink is pulled by the rounded edge R of the leading wiper blade to the next nozzle in the array, where it acts as a solvent to dissolve dried ink residue accumulated on the printhead face plate. The angular edge A of the trailing wiper blade then scraps the dissolved residue from the orifice plate. The black ink wiper has notches cut in the tip which served as escape passageways for balled-up ink residue to be moved away from the nozzle arrays during the wiping stroke.
Another wiping system using a spring-loaded, non-bending upright wiper was first sold in the Hewlett-Packard Company""s DeskJet(copyright) 660C color inkjet printer. Through a rocking action of the wiper blade and compression of the spring, manufacturing tolerance variations were accommodate for, including component variations in the service station, the Printhead carriage, and in the pens themselves.
Thus, there have been two major categories of wiper designs used in service stations in the past, namely (1) the flexible cantilever blade wipers, and (2) the spring-loaded, non-bending wipers. The cantilevered wipers relied on the compliance of the wiper material to provide enough normal force (the force perpendicular to the orifice plate) and enough frictional force to wipe ink residue and other debris from the orifice plate. The spring-loaded wipers used a shorter more rigid wiper, with the force applied to the orifice plate being controlled by selection of the spring. Both the cantilevered wiper and the spring-loaded wipers had difficulty cleaning across the raised encapsulant bead at each end of the orifice plate.
As illustrated in FIG. 8, inkjet printheads are constructed using a pair of encapsulant beads, such as bead E, which run along opposing edges of the silicon orifice plate P to cover the connections between the printhead resistors and an electrical flex circuit. The flex circuit delivers the nozzle firing signals from the carriage electrical interface to the printhead resistors. An energized resistor heats the ink until a droplet is ejected from a nozzle N associated with the energized resistor. The encapsulant beads E are typically constructed from an encapsulant material, such as an epoxy or plastic material. Unfortunately, the encapsulant beads E project beyond the outer surface of the orifice plate.
Due to the shape and location of the encapsulant beads, at the beginning of a wiping stroke the rounded leading edge of the cantilevered wiper blade initially contacts the orifice plate near the encapsulant bead, as shown in FIG. 8. As the wiper W2 traverses to the right in FIG. 8, there is a decrease in the normal force (the force perpendicular to the orifice plate) as the blade slides over the edge of the encapsulant bead E closest to the nozzles N. This decrease in the normal force as the blade leaves the encapsulant bead E may sometimes result in less effective wiping of the nozzles closest to the encapsulant bead. While this touchdown area T is relatively short, as new Printhead designs move the nozzles in closer to the encapsulant beads, a new wiping solution is needed to ensure that nozzles in the touchdown zone T are adequately wiped.
According to one aspect of the present invention, a wiping system is provided for cleaning an inkjet printhead of an inkjet printing mechanism having a chassis. The wiping system includes a sled supported by the chassis, and a wiper blade supported by the sled to engage and wipe the printhead through relative motion of the blade and the printhead in a wiping direction. The wiper blade has a wiping tip which defines a transverse groove running transverse to the wiping direction.
According to another aspect of the present invention, a wiping system is provided for cleaning an inkjet printhead of an inkjet printing mechanism having a chassis. The wiping system includes a sled supported by the chassis, and a wiper blade supported by the sled to engage and wipe the printhead through relative motion of the blade and the printhead in a wiping direction. The wiper blade has a leading surface, which encounters the printhead when wiping in the wiping direction, and a trailing surface opposing the leading surface. The leading surface and the trailing surface are joined at a wiping tip which defines a groove therein running between the leading surface and the trailing surface.
According to a further aspect of the present invention, an inkjet printing mechanism is provided including a wiping system, which may be as described above.
According to an additional aspect of the present invention, a method of cleaning an inkjet printhead of an inkjet printing mechanism is provided. The method includes the steps of providing a wiper blade having a first surface, and a second surface opposing the first surface, with the first surface and the second surface joining at a wiping tip which defines a groove therein running between the first surface and the second surface without intersecting at least one of the first and second surfaces. In a wiping step, the printhead is wiped with the wiper blade through relative motion of the wiper blade and the printhead. The method further includes the step of, during the wiping step, at least partially closing the groove.
An overall goal of the present invention is to provide a printhead service station for an inkjet printing mechanism that facilitates printing of sharp vivid images, particularly when using fast drying pigment based, co-precipitating, or dye based inks by providing fast and efficient printhead servicing.
A further goal of the present invention is to provide a method of servicing an inkjet printhead that is expediently accomplished in an efficient manner.